Roadway Grip Tester and Method

ABSTRACT

A method for measuring road surface friction of a road surface uses a vehicle that moves across the road surface wherein (1) an auxiliary independent wheel assembly is towed behind the vehicle and is in contact with the road surface, an auxiliary wheel of the wheel assembly is freely rotatable by movement of the vehicle and is one or more of toed in or toed out with respect to a direction of travel of the vehicle so as to create an isolated axial force on the auxiliary wheel: (2) the axial force on the auxiliary wheel is measured while the vehicle moves across the road surface, and the measured axial force is correlated with the road surface friction. The independent wheel assembly is load isolated from the weight of the towing vehicle and the independent wheel assembly is loaded by placing ballast thereon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional application Ser. No.60/758,047 filed Jan. 11, 2006, entitled “Roadway Grip Tester andMethod”, the disclosure of which is expressly incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND

Disclosed generally is a practical system of measuring road surfacefriction using an auxiliary wheel and more particularly to a systemwherein a switch in the cab deploys the measuring wheel and the in-cabdisplay gives a continuous reading of road surface friction as soon asthe wheel rotates. The road friction tester (“RFT”) is designed for usein the trucking industry to determine road surface grip where drivingconditions may be hazardous.

In U.S. Pat. No. 6,840,098 (the “'098 patent”, which is incorporatedherein by reference) the original GEM™ device is disclosed to include avehicle and a device for measuring road surface friction, which deviceis affixed to the vehicle. The device for measuring road surfacefriction includes an auxiliary wheel mounted to the vehicle and betweenthe vehicle and the road surface. The auxiliary wheel is toed in or toedout, loaded, and mounted on an axle for its free rolling. A calibratedforce sensor is associated with the auxiliary wheel to measure theisolated axial force thereon. A converter displays the road friction anddisplays it to the vehicle operator or remotely. The GEM™ device is usedfor measuring road surface friction of a road surface and uses a vehiclethat moves across the road surface. An auxiliary independent wheel isinterposed between the vehicle and the road surface. The auxiliary wheelis freely rotatable by movement of the vehicle and is toed in or toedout (skewed) with respect to a direction of travel of the vehicle so asto create an axial force on the auxiliary wheel. The axial force on theauxiliary wheel is isolated and measured while the vehicle moves acrossthe road surface. The measured axial force is correlated with the roadsurface friction.

While such design has been determined to work effectively andefficiently when used in conjunction with a snow plow or other heavyvehicle, a modified design was determined to be needed when the GEM™device was towed behind or mounted under a small vehicle, such as a SUV,pickup truck, or like light-weight vehicle, such as a passenger vehicleor car.

It is to such lightweight vehicle RFT device (the RT3™ device) that thepresent invention is based.

BROAD STATEMENT

A method for measuring road surface friction of a road surface uses avehicle that moves across the road surface wherein (1) an auxiliaryindependent wheel assembly is towed behind the vehicle and is in contactwith the road surface, an auxiliary wheel of the wheel assembly isfreely rotatable by movement of the vehicle and is one or more of toedin or toed out with respect to a direction of travel of the vehicle soas to create an isolated axial force on the auxiliary wheel: (2) theaxial force on the auxiliary wheel is measured while the vehicle movesacross the road surface, and the measured axial force is correlated withthe road surface friction. The independent wheel assembly is loadisolated from the weight of the towing vehicle and the independent wheelassembly is loaded by placing ballast thereon. A variety of improvementsare disclosed which have particular relevance when a normal passengervehicle (car, light duty truck, or SUV) is used to tow the RGT.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of the RGT mounted solidly to a lightweightvehicle (pickup truck) using stabilizer plates on each side;

FIG. 2 is a plan view of the RGT showing threaded stops to bearingposition to allow fine adjustment of toe angle of the RGT wheel for boththe under truck and tow behind versions;

FIG. 3 is an overhead perspective view of the RGT showing the swing armand swing arm pivot that permits facile changing of the RGT wheel forboth the under truck and tow behind versions;

FIG. 4 is a schematic of the load cell and stop layout for both theunder truck and tow behind versions;

FIG. 5 is a graph of the force factor plotted against the tread depthbased on an empirical tire wear algorithm;

FIG. 6 is a graph of friction plotted against road temperature;

FIG. 7 is an underneath perspective view of the RGT showing the multislots for variable height position;

FIG. 8 is a perspective view of the RGT showing the chain holding of thewheel for both the under truck and tow behind versions;

FIG. 9 is graph of the HFN Halliday Friction Scale™ based on anempirical algorithm;

FIG. 10 is flow diagram showing calculation of the empirical algorithmof Applicant's;

FIG. 11 is a flow diagram showing calculation of average road frictionwhen the RGT is fitted to dual or tandem wheels towed behind a passengeror other vehicle;

FIG. 12 is an overhead schematic of the tandem wheel arrangement of FIG.11

FIG. 13 is a side schematic of the tandem wheel arrangement of FIG. 12;

FIG. 14 is a sectional view along line 14-14 of FIG. 3;

FIG. 15 is a schematic of an alternative placement of the GEM device;

FIG. 16 illustrates yet another way of measuring axial load on the tireswhere the load cell is designed to remove any rotational forces on thebearings; and

FIG. 17 is an overhead plan view illustrating the permitted installationof the load cell assembly on an ordinary passenger car's front and/orrear wheel center and from this change in force, deduce the friction onthe roadway over which the vehicle is traveling.

These drawings will be described in further detail below.

DETAILED DESCRIPTION A. Roadway Grip Tester

While the '098 patent device is a substantial step forward in the art,it became apparent that design changes were required in order to makethe device more user friendly to automobile and truck, for example,drivers and in order to reliably measure smaller side forces between atoed wheel and the road surface. It is to such practice device that isdisclosed herein.

1. In General

Optionally, the RGT wheel can be towed behind or placed under a smallvehicle, as compared to being mounted on a large vehicle like asnowplow. For this to happen the side loads that can be used in thisapplication are significantly lower than with the snowplow type vehicle.This smaller side force is required such that the affects on the smallervehicle because of the RGT wheel present are reduced. This smaller forceis a result of doing two things: (1) placing a smaller vertical load onthe wheel and (2) reducing the angle of toe.

2. Ballast Weight & Shock Absorber Use

For the tow hitch type application, when considering the use of alightweight vehicle particularly, the constant vertical force requiredfor such an application should not be generated from using the vehicleweight in any way, since this will result in a reduction of verticalload at any of the vehicle tires which could result in a dangeroushandling condition for that vehicle, especially in low road gripconditions. This can be compensated somewhat by adding ballast to thevehicle; however, the variation in vertical weight on the RGT wheel thatensues with this method would not allow a constant friction measurementbetween tire and road surface. The solution to this problem is to useballast weight that can be placed close to the auxiliary wheel centerand for this weight to be relatively independent of the vehicle itself.This can be achieved by mounting the auxiliary wheel on a wishbone, asin the under truck model, placing ballast weights on the auxiliary wheelcenter, and inserting a shock absorber (or shock absorbing system)between the wishbone and the mount frame. The shock absorber allows theauxiliary wheel tire to traverse the road surface smoothly and notresult in bouncing of the wheel. This replicates very closely similarconditions as seen by a small vehicle tire. It also is possible thatthis use of ballast, instead of constant vertical load generated by ahydraulic cylinder, also could be used in the under-truck installationversion.

FIG. 1 shows the disclosed RGT, 10, that includes, inter alia, a rigidframe, 12, mounting to the vehicle, a wishbone frame, 14 (see FIG. 3), awheel/tire assembly, 16, and ballast weight, 18, towed by a vehicle, 20.A shock absorber, 22, accommodates any bounce of the wheel/tire assembly16 due to rough roads or the like.

3. Rigidly Attached Frame when Using a Single RGT Wheel

Auxiliary wheel assembly 16 requires that the wheel be rigidly attachedto the frame of vehicle 20 in order to maintain a consistent toe angle.This is achieved by attaching RGT frame 14 rigidly to vehicle 20framework by means of stabilizer plates, 24 and 26 (not shown), oneither side of the vehicle tow hitch assembly. It also is possible, butless practical, to incorporate the RGT frame as part of the vehicle towhitch assembly where it can be directly fastened to the vehicle chassis,i.e., the RGT frame replaces the vehicle standard tow hitch frame.

4. Small Side Force on Tow Hitch Version

The affects of the generated RGT side force on vehicle 20 cannot upsetvehicle 20 and/or the driver of vehicle 20. This requires that the toeangle of wheel assembly 16 cannot be large, i.e., the tow angle needs tobe in the order of about 1 to about 2 degrees relative to the vehiclelongitudinal centerline when using a normally available road car tire.It has been determined that the side force generated by auxiliary wheel(RGT) assembly 10 should not be in excess of about 175 lb when vehicle20 is driven in a straight line. For the road tire chosen, placing thewheel at about 1.5 degrees and using about 300 lb of dead weight(ballast) between the RGT tire and the ground achieves this.

5. Toe Adjustment

Each vehicle “tracks” slightly differently compared to other vehicles ofthe same or different type. For this reason, it is necessary, once theRGT wheel has been attached to the vehicle, that it be aligned at therequired angle to the towing vehicle in order to generate the desiredside force on a selected road surface. This is best achieved in one oftwo ways. Shims can be placed on either side of the GEM hub bolt faces.These are relatively close at about 10.25″ centers and awkward to adjustwhen all items are bolted to the GEM hub. The more desirable method, asillustrated in FIG. 2, is to, in plan view, rotate the whole wishbone byhaving the capacity to slide each of the 2 support hub assemblies, 28and 29 (see FIG. 3 also), mounted at each end of the wishbone fore/aftby undoing and then re-tightening the bearing mount bolts, as forexample for support bearing assembly 28, bolts 32 and 34, which permitssupport bearing assembly 28 to move within a pair of slots, 36 and 38.

6. Swing Arm—Easy Tire Replacement

It is desirable to be able to replace wheel/tire assembly 16 readily.Using a cantilevered system or a swing arm, 40, secondary support can dothis as illustrated in FIG. 3. A cantilevered system would require someredesign of '098 patent GEM hub to retain its rigidity with respect towheel position especially in toe control. Swing arm 40 is released byundoing a single bolt at the axle center and then pivots at the pivotcenter, 42, giving clearance to remove wheel/tire assembly 16.

7. High Resolution Load Cell

To obtain good accuracy and resolution of this force output, the loadcell cannot be of a high load value since any repeatability, accuracy,and temperature affects, etc., are as a % of the maximum load cellvalue. It is, thus, necessary that the load cell maximum load value beas low a possible. Because of this requirement, it is, therefore, veryeasy to overload the load cell, which has low maximum capacity.

The load cell and stop layout are illustrated in FIG. 4. Referringinitially to the load cell assembly, 44, the components are from top tobottom: a load cell clamp, 46; a load cell bushing, 48, a no load endfloat gap, 50; an end float shim, 52; a load cell washer, 54; aBellville load cell spring washer, 56; a face height shim, 58; a loadcell recess, 60; and a load cell indexing shim, 62. A load cell, 64, isdisposed next with lower load cell bushing, 66, completing the load cellassembly 44. The various bushings and washers can be of the Bellvilletype, i.e., spring loaded, which along with the stops retard overloadingof the load cell.

As shown in FIG. 14, hub assembly 30 is affixed to frame 14 and housesload cell assembly 44. Most of the automobile hub components (e.g., oilseals, bearings, races, and the like) are standard, such as seen in FIG.3 of the '098 patent, and will not be described in detail herein.Suffice it to say that load a isolating linear bearing assembly, 146, isintegrated into the hub assembly with all but axial forces (loads) beingisolated so that load cell assembly 44 measures road surface(frictional) forces, as disclosed herein.

8. Load Cell Bellville/Stop System

An auxiliary wheel mounted to a vehicle can experience relatively highside loads, if the wheel were to be dragged over curbing, etc. It is,thus, necessary to protect the load cell mechanically such that thishigh loading does not overload the cell beyond its maximum value. Awheel with some small toe angle can be subject to overload forces whenthe vehicle may catch a curb, etc. An apparent solution may be toincrease the capacity of the load cell.

Load cell load resolution enhancement: In order to gain the resolutionof force required when using a low force value in the Tow Hitch versionillustrated (or the under truck version of the '098 patent), we haveincorporated the use of a combination of Bellville washers and load cellin series and then this in parallel with mechanical stops. This isnecessary to obtain better load resolution. The Bellville washers areplaced in series with the load cell in both the compression and tensiondirections of load application on the load cell. As load is applied tothe cell, the Bellville washers compress as the load cell is measuringthe load. Eventually when the load is high enough the mechanical stopcomes up against the housing that supports the load cell and, thus,stops any further loading of the load cell, but allowing the load to betaken by the stop. Again, FIG. 4 illustrates the load cell and stoplayout.

9. Load Cell Temperature Gradient

The load cell load output value can be affected negatively by having atemperature gradient from one end of the load cell to the other end. Ifface ‘A’ happens to be hotter than face ‘B’ of the load cell, allowingtemperature to flow in the axial direction of the cell, during thistransition stage whilst the cell is gaining equilibrium temperature theload readings from this cell will be erroneous. The higher the load cellrating the worse will be the affects of this value—typically quoted as a% of full load value. To reduce the transient affects of heat flow tothe load cell a temperature inhibitor (titanium in this case) is placedon either side of load cell assembly 44, isolating the cell from the hotand cold faces.

10. Tire Wear Algorithm

With a treaded tire, as the tire wears and the tread depth decreases,the side force between tire and road surface changes. Because of thisvariation, it is necessary to include compensation for tire wear withmileage, i.e., as the tire wears the measured force is modified by amultiplier factor based on values for the respective tire used. Forinstance, for a particular tire with a nominal tread depth of 4.0 mm thetrue force between the tire and the road surface is multiplied by afactor of 0.758 in order to give the corrected friction value on thedisplay. This is performed through an algorithm imbedded in the softwarewithin the display. The tire wear algorithm is displayed in FIG. 5,where tread depth (mm) is plotted against the force factor. Thisalgorithm will change depending on the brand of tire used.

11. Tire Distance Measured for Tread Compensation

It also is very desirable to not have to continually enter the treaddepth of the auxiliary wheel tire as it wears. Inside the software, isimbedded a tire wear rate algorithm. As long as the tire mileage ismeasured the tread depth can be calculated. For this reason, inside theGEM force hub is located a rotational displacement sensor which is usedin conjunction with the display software to calculate the predictedtread depth and uses this value in its calculation adjustment for treaddepth. The software is capable of having the wear rate mileage changedby the operator, since tread wear rate is dependent on the surface overwhich the tire runs. At any time, the tire tread depth can be measuredand the correct tread depth entered into the software.

12. Road/Tire Temperature

If the road or tire temperature were measured, another adjustmentalgorithm could be incorporated into the software to allow acompensation of the friction force reading, as is indicated in the FIG.6 (where road temperature, ° F., is plotted against friction) whichshows the variation of friction force generated with variation in roadtemperature for the particular SE 200 Bridgestone tire used currently.This algorithm would change on the tire being used.

13. RGT Mount Frame Height Adjustment

The height of the tow hitch varies between vehicles to which the RGTunit is fitted. It is necessary that the RGT mount frame be positionedat a relatively consistent height relative to the ground. For thisreason it is necessary to allow for this height change with the centraltow hitch being adjustable to the RGT mount frame as shown in FIG. 7.Use of a series of vertical slots, such as a typical slot, 70, permits ahitch plate, 72, carrying the hitch tongue, 74, to be adjustedvertically, which in turn adjusts the vertical height of RGT unit 10.

14. Cantilevered RGT Wheel

It is possible, if the RGT wheel has good toe control, to have a fullycantilevered GEM assembly that would allow easy wheel replacement. Thiswould eliminate the need for a swing arm type arrangement. Thiscantilevered assembly is readily done with the friction load beingmeasured in the GEM hub with a similar arrangement, as shown in FIGS. 15and 16 for a hub assembly, 150 (this system is one that could beincorporated on any road car to measure the roadway friction as shown inFIG. 17). In FIG. 3, there would not exist any swing arm. The slottedtow adjustment would still be required, however.

The unit illustrated in FIGS. 15 and 16 was mounted on a passengervehicle and evaluated. RGT assembly 150 includes a load cell assembly,152, as described elsewhere herein including with reference to FIG. 14;a load isolating bearing assembly, 154; wheel bearings, 156; rotatinghub, 158; and steering knuckle, 160.

15. Use of Grip Information

Since the road friction value can be measured in a dynamic mode, it ispossible to have a reactive loop feeding from this reading. Forinstance, the automated deployment of material to the road surface basedon the friction reading is possible. An operator, then, can override incase the conditions subjectively referenced are different from thefriction measured. For instance with fresh snow on the ground, theoperator may wish to plow the snow from the surface before deploying anyproduct. Also, a factor that can affect this is that the productdeployment point and the point of friction measurement on vehicles canvary.

16. Steering Affects

Since the friction result is generated by means of a tire being scrubbedalong the road at a small tow angle, any steering of the vehicle canchange this friction value. As the vehicle steers to the left thefriction reading may increase and vice versa when steered to the right.The rate at which this friction force changes can be directly correlatedto the amount the vehicle is steered and the speed at which the vehicleis traveling. For this reason, if the steering angle is measured, we cancorrect in the software with a multiplier for this unwanted frictionvalue change. In its simplest form, the steering input can be used toremove unwanted friction results due to vehicle steering by having thefriction result not show any values after a predetermined steering valueis achieved in the vehicle in either direction. For either system itwould be necessary to calibrate each vehicle steering sensor to thefriction display software. The friction correction can be made with thesteering input only or with the steering and speed inputs as themultipliers together.

17. Chaining Up RGT Wheel

It may be desirable not to run the RGT wheel on the ground for somereason i.e., for example, if one does not wish to wear the RGT out. Inthis case, it is possible to chain the RGT wheel up off the ground witha chain, 80, as shown in FIG. 8.

18. Alternative Load Cell Placement (Torque Measurement)

When a tire is toed relative to the direction that the vehicle istraveling in plan view the loads between the tire and the road are twofold; an axial force is generated at the axle center and a rotationaltorque is generated about the center of contact between the road and thetire. Up till now, we have considered how the axial force is measured.We can also measure the result of this torque (which is an indication offriction force between tire and road) by measuring the load on somesuspension component (steering tie rod at the front or toe control rodat the rear). It is likely that this load is best measured with a methodthat encompasses a safety stop system with a high resolution load cellas is used when measuring the axial force. Note that in the RGT systemone can replace the GEM hub and place the load cell in any part of theindependently supported suspension system where the axial force can becalibrated, i.e., the wheel does not need to be cantilevered to placethe load cell elsewhere. In an application where the friction ismeasured continuously by means of a wheel that is toed relative to thevehicle center, it is possible that the load that is measured can be atan alternate position other than the GEM hub. It is possible that theload cell can be placed within a strut of the support for the frictionwheel such that this torque force can be measured and thus calibrated tothe friction force between the tire and the road. The leg of thewishbone as indicated in FIG. 17, for example. Through the software,this load measured can be calibrated to the side force reaction load(friction force) between the tire and the road.

19A. Friction Scale (Halliday Friction Number™—HFN™)

A friction scale is available that references the side force between thetire and the road surface. This scale is a linear relationship betweenthe number and the road surface tire axial side force. That no forcebetween the tire and the road be 0 and that 100 be that side forcebetween the tire and the road when the tire is being run on tarmac thatis free from contamination and that the surface be relatively smooth.This value of 100 can be for a road at a particular temperature or itcan be a number that is manipulated to take account of the roadtemperature by using a multiplier as per the temp graph. This isillustrated in FIG. 9, where for plot, 90, the different road conditionsare shown for: dry cold road at 30° F., 92; dry hot road at 96° F., 94;1 inch snow on clean tarmac, 96; intermittent ice, 98; and ice, 100.

Taking into account a tread modifier, a temperature modifier, a speedmodifier, and a steering value modifier, the friction value of a roadsurface can be measured directly or can be mathematically treated withthe listed modifiers to derive a friction value of a given road surface,as illustrated in FIG. 10.

19B. RGT Marker Wand

Having a sprung loaded fire hydrant type marker placed on the RGT wheelassembly also is a good idea, because it serves two purposes: the first,being a visual reminder of the presence of the RGT wheel whenmaneuvering the vehicle; and the second, being a roughness indication ofthe surface of road over which the RGT wheel is moving this beingindicated by how vigorously the wand is moving.

20. RGT System not Rigidly Mounted to Vehicle Frame

For general transport and airport use, it is possible that the agencymay require a unit that has more accuracy and also has the ability tomeasure surface friction whilst the vehicle towing the RGT wheel isturning. For this reason, it is possible that a dual wheel system (seeFIGS. 12 and 13) could be used within a system that is not rigidlyattached to the vehicle frame in the toe alignment direction. This“trailer” system could be toed behind a vehicle with either two separateGEM systems, one for each wheel, or a single GEM system accepting axialloads from each of the two wheels. In either system the net force can bemeasured and used under all conditions including cornering of thevehicle. This system would allow the road friction whilst cornering tobe measured more accurately than with the original GEM system. Thissystem will allow the road friction to be measured around corners. Itcould be required that for convenience both RGT wheels be capable ofbeing aligned independently of one another relative to the vehicle. Withthis the force input from a left RGT wheel assembly, 110, and a rightRGT wheel assembly, 112, could be averaged to give a net output of grip.This would happen because the right wheel would be toed in/out and theleft wheel would be the opposite toe angle. This system would use manyof the enhancements of the single wheel RGT unit, as disclosed elsewhereherein.

It also is possible that the two wheels could have their toe angles setrelative to one another since the two tires would align themselvesrelative to the vehicle, as a unit at such an angle to the vehiclewhereby the RGT twin wheel unit may be at some small angle relative tothe towing vehicle when being driven in a straight line.

It is desirable to place shock absorbing system, 114, at the center ofthe assembly and adjacent to the ballasts, 116 and 118, such that theshock forces go directly through the twin pivot assembly to the towvehicle and do not create undesirable force moments on the twin wheelsupport frame. For ease of backing the unit particularly, one or bothsides of the twin wheel frame should be connected to the tow vehicleframe. The RGT unit could be placed on the inside of each wheel assemblywith a representative RGT unit, 120, being illustrated in FIGS. 12 and13. Again, swing arms, 122 and 124, could be used as described herein.

The friction value of a given road surface can be determined, forexample, by averaging the two values measured for each wheel assembly,such as illustrated in FIG. 11.

B. Safer Car when Used in Slippery Conditions Problem

Many attempts have been made to use the change in speed of a vehicleswheel to indicate roadway friction conditions, i.e. the variation in thehigh-resolution rotational speed measurement at each wheel. Generally, avehicle will not experience rotational slip when the vehicle istraveling at relatively constant road speeds (as experienced when in“cruise” mode, for example). This rotational speed variation can verylikely be used in association with the vehicles acceleration (ordeceleration) to determine road conditions. This condition does notexist when a vehicle is in a non-accelerative mode, for instance, whichis a lot of the time in the USA. For this reason, there needs to be someother sensor input that allows the road surface condition to be measuredand then indicated to the driver of the car or for the car to becontrolled automatically to a safer state.

It is important to realize that a road tire does not transition torotational slip gradually, i.e., the tire grips or it does not grip inthe rotational tractive/braking mode. However, during our investigationof the side forces measured on a road tire, the side or axial force iscontinually changing as the tire rotates the tire continually grips thenlets go as it rotates. For this reason it is far better to use thisforce variation to determine the surface friction of the road than it isthe change in rotational torque indicated by measuring wheel speeddifference. This side force as well as continually gripping and lettinggo also grips with less or more force depending on the surface changingover which it is rolling.

Based on experience of the RGT and GEM inventions, it has becomeapparent that on any road vehicle the use of side force and tire torque(in plan view) on a tire (any of the vehicle tires, but most likely reartires) can be used to give to the operator of the vehicle an indicationof the friction value between the vehicle tires and the road surface.That is, if one can measure the side load or torque in plan view at eachof the rear tires and an algorithm can be created to indicate a directreference to road friction, then an audible or visual indicator can bedirected to the operator of the vehicle to allow the vehicle to beoperated with more safety.

With the RGT, a dry road force axial force of 115 lb on a singlestandard road tire is used to indicate a ‘good’ friction value and whenon an ice surface the friction force falls to a value of approximately20 lb, i.e., 15% to 20% of the value for dry warm pavement.

The angle of this tire on the RGT is approximately 1.00 degrees to thestraight-ahead condition. On a typical car rear tire (for example, aHonda Accord Rear tire) each rear tire is toed in at approximately0.080″ over a 16″ distance (rim diameter). This results in an angle ofabout 0.25 degrees on each rear tire, i.e., ¼ of the angle used on theRGT.

The vertical load on the average rear tire would be higher than the 400lb used for the RGT. If the load is say 800 lb (some SUV vehicles wouldbe above 1200 lb on each rear corner) and the angle is ¼, it is likelythat the tire side load of the SE200 tire is approximately 50 lb on dryroad (and greater for a larger tire).

This would result in an ice load of about 10 lb and the car RGT typesystem would have to have good resolution and mechanical stops to beable to measure the difference between the 50 lb and 10 lb loadspredictably and, yet, still be capable of resisting the high side forcesexperienced by the rear tires of the vehicle.

As with the existing invention with the GEM hub, the car system wouldneed to incorporate a good resolution load cell with mechanical stopswith only small axial displacements such that any braking system is notaffected negatively. These small axial movements required of this systemwould require as is standard on most cars, a floating caliper/brake padsystem. The anticipated axial movement would only be required to be inthe order of ±0.010″.

All of the discussion above references to a small vehicle traveling in astraight line whereby the vehicle may have about a 50 lb (dry road) sidetoe load inward to the vehicle centerline at each rear wheel. This forceon each side would drop to about 10 lb; thus, referencing the slipperyconditions. These forces are rather low and so an artificial method ofincreasing these forces should be investigated. Some examples of howthis small force can be remedied are indicated below.

It is most likely that for winter conditions that a special winter tirecan be used or developed. The special qualities of this tire would be asfollows:

-   -   More grip at lower temperatures (as is the case with the SE200        Bridgestone)    -   Be installed on the vehicle in a fixed orientation with a biased        tire build that would allow a significantly higher axial load        than the estimated 50 lb on dry road (say 100 lb) without        negatively affecting the cars handling characteristics.    -   The Firestone road course rear tire for instance on an Indy type        car produces several 100 lb side load pushing to the racecar        center, i.e., toe in load and the car handles perfectly OK.    -   It is also possible that for winter use the rear toe angle can        be changed automatically to a more toe in condition for adverse        conditions—some of the GM products having active steering at the        rear, for example, which cold accommodate such an angle change        as a winter mode, possible. Another method for measuring the        axial load is illustrated in FIG. 16. Also, this load possibly        could be measured within the tire itself and be used in the        manner described above. This unit type would be used with the        original GEM device.

If this information on friction value is accurately gathered by thevehicle, then it is possible that this friction information can be sentthrough a phone link (“ON STAR” or other satellite service) to a centralgroup that uses this friction information to indicate by signage toother road users or as can be used with the RGT a direct link to a‘smart sign’ such that other vehicles can be directly informed of poorroad conditions.

There always is the possibility that a reactive feed back loop can beused directly on the vehicle or externally fed from a central offvehicle station to force the vehicle to travel at a speed appropriate tothe conditions, i.e., slower if more slippery.

All 4 corners (or a single corner) of the car can have the axial load ortorque in plan view measured and an algorithm can be incorporated toallow the road conditions to be measured as the car corners.

It also is possible to have the road friction condition referenced byjust using an axial load measurement off each rear wheel only. Theinputs required for this algorithm could include steer angle, vehicleacceleration in any of the three axes, throttle angle (engine torque),gear, and speed.

C. Safer Car Braking

PROBLEM TO OVERCOME: When braking a vehicle, the driver may apply moreor less pressure to the brake pedal in order to stop the car dependenton the requirement of the situation.

In this situation the driver of the car following the vehicle, which isbraking, is often unable to see around/through the vehicle doing thebraking and/or sense the rate of deceleration of the car and so isunaware soon enough of the braking requirement he has. This inability tosense what the rate of deceleration is of the car ahead is worsened whenthe conditions and visibility get worse. This I think is one the reasonsso often why vehicles crash into one another nose to tail.

When the brake lights come on in the car in front presently it is asingle message to the driver behind, i.e., brakes on (lights on) orbrakes off (lights off). This signal does not give any degree ofdeceleration of the vehicle which is slowing other than a sense of thevisual deceleration of the vehicle which at times is difficult to sensedirectly especially in the dark and other adverse driving conditions.

In some newer vehicles, there exist vehicle systems that position atrailing vehicle relative to the vehicle in front by having activeproximity sensors to allow this positioning. When in close proximitytraffic any sensor of this type may become annoying as most travelerstravel too close to the vehicle in front.

It would be advantageous to have a system (possibly light) at the rearof the vehicle that is representative of the degree of deceleration ofthat vehicle. This can be initiated by an in car accelerometer and/orbrake pressure, i.e., the higher the deceleration or braking hydraulicpressure used, the greater the indicator should be the indicator on therear of that vehicle to the vehicle behind it. Most likely it should bea combination of these two sensors since the vehicle may not be slowingfast enough because it is on a surface that does not have the frictioncapability. In this case the added input of an activated ABS couldtrigger this warning to the trailing vehicle.

I suggest that the present brake light system be extended to incorporatea greater number of lights (perhaps 3), i.e., more lights on when thevehicle is slowing at a greater rate and all of the lights on when thevehicle has stopped. Also, it would be possible to have these lightsflashing when the deceleration gets beyond a preset value. That is ifthe deceleration is greater than say 0.5 g then the lights flash as thecar is slowing. Alternatively, different color lights green, yellow,red—when all 3 lights are on the greater the deceleration of thevehicle, etc.

Because of the ability of the proximity sensors to control a vehiclesposition, it also is possible for this following vehicle to measure therate of deceleration of the vehicle it is approaching and for some typeof signal be indicated to the driver of that following vehicle to allowhim time to brake his vehicle. This rate of declaration can be linked tothe speed of the traveling vehicle and by means of an algorithmassociating vehicle speed, rate of approach to the vehicle in front. Thevehicle could be decelerated automatically or a series of indicatorscould be shown the following vehicle driver. The greater the requirementto slow the vehicle the greater should be the indication to slow thevehicle. This indication could be in the form of a series of lightswhereby the more lights that are on the greater the requirement to slowthe vehicle or as an audible output.

While the invention has been described with reference to variousembodiments, those skilled in the art will understand that variouschanges may be made and equivalents may be substituted for elementsthereof without departing from the scope and essence of the invention.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed, but that the invention will include all embodiments fallingwithin the scope of the appended claims. In this application all unitsare in the American system and all amounts and percentages are byweight, unless otherwise expressly indicated. Also, all citationsreferred herein are expressly incorporated herein by reference.

1-32. (canceled)
 33. A method for measuring road surface friction of aroad surface using a vehicle that moves across the road surface saidvehicle having one or more independently suspended wheel assemblieshaving an axle and an axle support, which comprises the steps of: (a)fitting one or more of each independently suspended wheel assemblies ofsaid vehicle with an assembly that that measures axial force between theaxle and the axle support of said vehicle; and (b) measuring said axialforce as said vehicle moves across a road surface; and (c) correlatingsaid measured axial force with the road surface friction of said roadsurface.
 34. The method of clam 33, wherein larger measured axial forcescorrelate with greater road surface friction and smaller measured axialforces correlate with smaller road surface friction.
 35. The method ofclam 33, wherein said vehicle is driven in a straight line direction,opposite wheel assemblies are fitted with said axial force measuringassemblies, and the measured axial forces are compared to determine theroad surface friction.
 36. The method of clam 33, wherein toe angle ofat least one of said wheel assemblies is set to be greater during winterdriving then during summer driving of said vehicle.
 37. The method ofclam 33, wherein the measured road surface friction is communicated to adriver of said vehicle or to a remote location.
 38. A method forsignaling a second vehicle driver driving a second vehicle on a road andfollowing a first driver driving a first vehicle on said road, whichcomprises providing a visual display in said first vehicle to saidsecond driver correlative to the degree to which said first vehicle isdecelerating.
 39. The method of claim 38, wherein deceleration of saidfirst vehicle is determined by one or more of sensing change in wheelspeed, actual sensed values from the change in rotational speed of awheel, an accelerometer, a decelerometer, or actual sensed values of thebrake pressure applied by the first driver.
 40. The method of claim 38,wherein said visual display comprises a grouping of lights displayed tosaid second driver wherein more lighted lights correlates with increaseddeceleration.
 41. The method of claim 38, wherein said visual displaycomprises a grouping of lights displayed to said second driver whereindifferent colored lighted lights correlates with increased deceleration.42. The method of claim 38, wherein the second vehicle is fitted withdisplacement sensors to determine the proximity of the first vehicle andsaid first vehicle senses above normal deceleration and that this sensedvalue of deceleration is used to one or more of visually or audiblyindicate to the second driver the rapid closing of the distance betweenthe two vehicles or that this sensed value be used to automaticallydecelerate the following vehicle.
 43. A method for measuring roadsurface friction of a road surface using a vehicle that moves across theroad surface said vehicle having one or more independently suspendedwheel assemblies having wheel centers, which comprises measuring theaxial force at one or more wheel centers.
 44. A method for measuringroad surface friction of a road surface using a vehicle that movesacross the road surface said vehicle having one or more independentlysuspended wheel assemblies having an axle and an axle support, whichcomprises measuring the load on one or more of said struts.
 45. A methodfor measuring road surface friction of a road surface using a vehiclethat moves across the road surface said vehicle having one or moreindependently suspended wheel assemblies having an axle and an axlesupport, which comprises sensing the torque change (in plan view) bymeasuring a load on one or more of said struts.